Species-specific description:
A segregation analysis of Icelandic sheep by Jonmundsson and Adalsteinsson (1985) provided substantial evidence for a gene of large effect on litter size. These authors named the gene Thoka, after the ewe from which the gene appears to have originated. Heterozygotes give birth to an extra 0.64 lambs, on average. In a segregation analysis of data from a Cheviot flock into which the Thoka gene was introduced via Icelandic rams, Walling et al. (2002) confirmed the existence of a gene of large effect on fecundity, but there was some evidence that this gene was present in the flock before the Icelandic introduction. Since this evidence is only preliminary, the gene will be assumed to be Thoka until further evidence is assembled [FN 13 Jan 2003]

Inheritance:
Just as in Fecundity, Cambridge (OMIA 000384-9940), which involves the same gene (GDF9), ewes heterozygous for the Thoka mutation in GDF9 show increased fecundity, but homozygotes for the same mutation are sterile.

Molecular basis:
Nicol et al. (2009) identified the causal mutation of Thoka fecundity as "a single base change (A1279C) resulting in a nonconservative amino acid change (S109R) in the C-terminus of the mature GDF9 protein, which is normally expressed in oocytes at all stages of development".

Variants

By default, variants are sorted chronologically by year of publication, to provide a historical perspective.

Readers can re-sort on any column by clicking on the column header. Click it again to sort in a descending order. To create a multiple-field sort, hold down Shift while clicking on the required column headers